Polyolefin graft polymers formed by grafting phenolic ester monomeric compounds, such as 4-acetoxystyrene, to polyolefins are known. The deacylated derivatives of these polymers have potential value as adhesion promoters and compatibilizers in applications requiring an adhesive bond or a compatible blend between dissimilar materials. These polyolefin graft polymers may be useful as adhesion promoters and compatibilizers with metal and polyester substrates, for which currently available grafted polyolefins, such as those grafted with maleic anhydride, do not perform well. The phenolic ester grafted polyolefins of the invention may also be further derivatized to make other useful products, including polymeric antioxidants and ion exchange media for separations.
Methods for preparing hydroxystyrene and dihydroxystyrene grafted polyolefins for use as ion exchange membranes are known (Fujiwara et al. U.S. Pat. Nos. 4,011,147 and 4,025,401). In those methods, a polyolefin film is subjected to ionizing radiation, such as gamma rays, X-rays, alpha rays, or electron beams, and then immersed in a solution containing a hydroxystyrene or dihydroxystyrene monomer. Alternatively, an acyloxystyrene or a diacyloxystyrene monomer is used. In that case, the grafted acyloxy group is hydrolyzed to convert the acyloxystyrene or diacyloxystyrene to hydroxystyrene or dihydroxystyrene, respectively. Because these methods use a polyolefin film, the grafting is limited to the surface of the film.
Melt grafting methods for making grafted polymers with phenolic ester monomeric compounds are known. For example, Suzuki et al. (JP 52004589) describe a melt grafting method for preparing a grafted hydrocarbon or fluorinated polymer by radical graft polymerization with at least one reactive monomer under high pressure in the presence of a radical initiator. In the melt grafting method, the polymer and the reactive monomer are mixed together in the presence of a radical initiator at a temperature of 150 to 220° C., which renders the material workable in extruders, mixers, etc. Optionally, the grafting may be done in the presence of an organic solvent that dissolves the reactive monomer and the radical initiator, and which swells, but does not dissolve the polymer. The reactive monomers used in that method include aromatic monomers having a polymerizable double bond, such as styrene, hydroxystyrene, dihydroxystyrene, and acyloxystyrene. The graft polymerization reaction requires high pressure, specifically, 50 to 15,000 kg/cm2. Additionally, Wilkey (U.S. Pat. No. 5,266,635) describes a melt grafting method for making hydrogenated styrene/diene copolymers having grafted 4-hydroxystyrene groups. The hydrogenated styrene/diene copolymers are grafted with 4-acetoxystyrene, which is converted to 4-hydroxystyrene by aminolysis, hydrolysis, or saponification. The grafted polymers are used to improve the low temperature impact strength of polycarbonates when the phenolic groups are reacted with the polycarbonates.
Methods for solution grafting of polyolefins with vinyl monomers in the presence of radical initiators are also known. However, these methods have not been used to graft phenolic ester monomeric compounds on polyolefins. For example, Ryoji et al. (JP 2000239479) describe a solution grafting method for preparing graft ethylene polymers using vinyl monomers, such as styrene, acrylonitrile, acrylic acid, and methacrylic acid, using a radical initiator. In that method, the polymer, vinyl monomer, and the radical initiator are dissolved in an inert solvent and the graft polymerization reaction is carried out at 50 to 180° C. in a plug flow reactor. Similarly, Fournier et al. (CA 1003145) describe a solution method for making graft polymers. In that method, rubbery ethylene-propylene copolymers are grafted with vinyl monomers such as styrene, vinyl chloride, methyl methacrylate, acrylonitrile and mixtures thereof, in the presence of a radical initiator in an organic solvent.
Therefore, the need exists for adhesion promoters and compatibilizers in applications requiring an adhesive bond or a compatible blend between dissimilar materials, particularly with metal and polyester substrates.
Applicants have solved the stated problem by providing a solution grafting method for making polyolefin graft polymers by grafting a phenolic ester monomeric compound on olefinic polymers in the presence of a radical initiator in an organic solvent. These grafted polymers provide improved adhesion to metal and polyester substrates.